Patent GB-1285068-A (GB)
Title: Battery charging arrangements
IPC: H02J7/00
Filed: 1969-10-14
Abstract: 1285068 Battery charging systems SOC DES ACCUMULATEURS FIXES ET DE TRACTION 14 Oct 1969 [15 Oct 1968 6 Aug 1969] 50509/69 Heading H2H A battery charging apparatus capable of charging a battery at a high rate or a low rate comprises a first element for sensing ambient temperature and a second element for sensing the internal temperature of the battery, control means for putting the apparatus into the low charging rate when the difference between the two sensed temperatures reaches an upper value and into the high charging rate when the difference reaches a lower value together with timing means for timing a period starting from the commencement of a charging of the battery which means are effective to lock the apparatus in the low charging rate condition at the end of the period. A battery B to be charged from an A.C. source by way of a charging circuit Ch is provided with a sensor S2, in the form of a positive temperature coefficient resistor, which is sensitive -to the battery temperature, a further sensor S1, similar to the sensor S2, being provided which is sensitive to the ambient temperature around the battery. The output signals of the two sensors S1, S2 are applied to a differential amplifier comprising transistors T1, T2 the output of which amplifier in turn controls transistors T3, T4, T5 the latter of which controls the charging circuit Ch to switch from a high charge rate to a relatively low charge rate. Assuming a condition in which the battery temperature is low the signals from the sensors S1, S2 will be such as to cause the differential amplifier to have an output at the collector of transistor T2 such that the collector current of transistor I3 will increase and when this current reaches a given value transistor T4 will become conductive and likewise transistor T5. When the transistor T5 is conductive it is effective to cause the circuit to switch to "high rate" thus charging the battery B at a high rate. The battery temperature will then increase until a point when the sensor S2 will provide a signal such that the output from the differential amplifier T1, T2 will fall to a point where the collector current of transistor T3 will become such that transistor T4, and hence transistor T5, will cut off and the charging circuit then switches to "low rate". The operation under the control of sensors S1, S2 is overridden by a timing device such that after a predetermined time the charging circuit Ch is switched continuously to the "low rate" condition. The timing device comprises two cells BO1, BO2 and transistors T7, T6. At the beginning of a charging process of the battery B a cell, say BO1, is assumed to be fully charged. With the cell BO1, charged a transistor T7 will be rendered conductive thereby blocking transistor T6. With transistor T6 blocked the control of transistor T5 is provided by the sensors S1, S2. As the cell BO1 discharges a point is reached when transistor T7 becomes non-conductive and transistor T6 conductive. Conduction of transistor T6 blocks transistor T5 thus switching the charging circuit to the "low rate" condition. The time delay introduced by the discharge of the cell BO1 is of such duration that the battery B reaches full charge before the charging circuit is switched to the "low rate". In a system wherein the battery B is used as a standby supply for a system having a normal A.C. supply, each failure and re-establishment of the A.C. supply causes one of the cells BO1, BO2 to be put on charge whilst the other is supplying the delay. In other embodiments the sensors S1, S2 may comprise temperature sensitive transistors which may be associated with an electromagnetic or electronic type switch. Furthermore the ambient sensor S1 may advantageously be associated with a body having a thermal inertia comparable with that of the battery and the body may be provided with an auxiliary heater to give an operational bias.